In recent years, a thermally assisted magnetic recording has been proposed as a means of realizing high recording density of 1 Tb/in2 or more (H. Saga, H. Nemoto, H. Sukeda, and M. Takahashi, Jpn. J. Appl. Phys. 38, Part 1, and pp. 1839 (1999)). In conventional magnetic recording apparatuses, when a recording density is 1 Tb/in2 or more, there is a problem that recorded information is lost due to a heat fluctuation. In order to prevent this, it is necessary to increase a coercivity of a magnetic recording medium; however, there is a limit to the magnitude of the magnetic field that a recording head can generate, hence, it becomes impossible to form a recording bit on a medium when the coercivity is increased too much. To solve the problem, in the thermally assisted recording, a medium is optically heated at the moment of recording to reduce the coercivity. Due to this, it become possible to record on a medium with a high coercivity and thereby to realize recording densities of 1 Tb/in2 or higher.
In the thermally assisted magnetic recording apparatus, a spot diameter of a light to be irradiated needs to be the same extent as that of a recording bit (several tens of nanometers), because a larger spot diameter eliminates the information in adjacent tracks. To heat such a microscopic region, an optical near-field is used. The optical near-field is a localized electromagnetic field (light of which wave number includes an imaginary component) that exists near a microscopic object of a size smaller than the wavelength of light; and the optical near-field is generated by using a microscopic aperture of a size smaller than the wavelength of light or a metal scatterer. For example, the Technical Digest of 6th international conference on near field optics and related techniques, the Netherlands, Aug. 27-31, 2000 p. 55, proposes an optical near-field generator that employs a triangular metal scatterer as a high-efficiency optical near-field generator. When the metal scatterer is irradiated with a light, plasmon resonance is excited in the metal scatterer, generating a strong optical near-field at the apex of the triangle. Use of such an optical near-field generator enables highly-efficient collection of light in a region of less than several tens of nanometers.
To achieve the above thermally assisted magnetic recording, it is necessary to optically heat a recording medium near a magnetic pole for applying a magnetic field. To realize this, for example, a waveguide is formed beside the magnetic pole such that a light from a semiconductor laser that is a light source, is guided to a position near the tip of the magnetic pole. In the case, the semiconductor laser is located, for example, at the root of a suspension, and a light is guided from there to a flying slider using the waveguide made of optical fiber, etc. (Kenji Kato et al., Jpn. J. Appl. Phys. Vol. 42, pp. 5102-5106 (2003)).